An innovative evaluation method based on polymer mass detection to evaluate the contribution of microfibers from laundry process to municipal wastewater.

Clothes washing releases numerous microfibers, including microplastic fibers (MPFs). Although MPFs in laundry wastewater are an important source of microplastics (MPs) in wastewater treatment plants (WWTPs), credible quantitative assessments of their contributions remain limited. Polyester fiber is the most important textile fiber. Its component, polyethylene terephthalate (PET) polymer, can be quantified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The release of MPFs from polyester clothes through washing was quantified via simulation experiments, and the MPFs in two WWTPs were measured by microscopic counting and LC-MS/MS. Direct comparison of the abundances of PET MPFs in laundry wastewater and WWTP influents led to an undervalued contribution rate of 9%-11% of the PET MPFs in laundry wastewater to those in WWTP influents. However, comparison of the mass of PET MPFs in laundry wastewater and WWTPs influents revealed that the PET MPFs from laundry contributed approximately 50% of those in the WWTPs. The latter was confirmed by comparing the number of polyester fibers released during clothes washing to the calculated number of "model MPFs" in WWTPs according to the PET mass concentration. Based on the PET concentration, the annual discharge of PET MPs from WWTPs to the water environment could also be estimated.